1. Field of the Invention
The present invention relates to a method and apparatus for pressure-welding an insulated electric wire to a pressure terminal by pressing the wire against the pressure cutters of the pressure terminal mounted in a connector housing in such a manner as to prevent the pressure cutters of the pressure terminal from being deflected outwardly when the covered wire is forced into the pressure terminal.
2. Related Art
The method of pressure-welding an insulated wire to a pressure terminal normally comprises the steps of placing the insulated wire on flat plate-like pressure cutters each having U-shaped slots, and forcing the insulated wire into the slots with pressure-welding dies. During the pressure-welding operation, the edge of the pressure cutter cuts the insulation to expose the conductors such that the conductors electrically contact the edges of the pressure cutter which define the slot.
FIG. 12 illustrates such a conventional arrangement where a pressure-welding die 104 forces the insulated wire 103 downwardly into engagement with pressure terminal 105 in a condition in which the pressure terminal 105 has been previously mounted in the terminal container 107 of a connector housing 106.
As shown in FIGS. 13 and 14, the pressure-welding die 104 has an arcuate pressing portion 112 for pressing against the wire such that the wire 103 is received in the U-shaped slot 101 of pressure cutters 102. At this time, the edge of the U-shaped slot cuts open the insulation of the wire 103 so that the conductors electrically contact the edge defining the U-shaped slot 101 and are retained thereby.
As shown in FIG. 15, when the pressing portion 112 of the pressure-welding die 104 presses the insulated wire 103 into the slot 101, opposing forces E are applied against the sides of the pressure cutter 102 tending to force them outwardly. If the arcuate pressing portion 112 of the pressure-welding die 104 keeps pressing the insulated wire 103 downward in the illustrated state, the insulation of the wire 103 will be torn by the edge of the U-shaped slot 101. When the arcuate pressing portion 112 presses the insulated wire 103 further downward, the conductors of the insulated wire 103 contact the edge of the U-shaped slot 101 and are retained thereby with a proper pressing force. Good electrical contact can thus be established. FIG. 13 shows a normal pressure-welding condition thus attained.
However, the conventional wire pressure-welding method experiences problems when, for example, the thickness and strength of the insulation are too great, the configuration of the edge of the U-shaped slot 101 is such that sufficient cutting-open force is not achievable or the strength of the pressure cutter 102 is low.
In other words, if the sides of the pressure cutter are bent outwardly in the manner shown in FIG. 16 there is a possibility that the insulation may not be completely torn so that electrical contact will not established between the conductors and the pressure cutter 102.
For example, when the insulated wire 103 has a diameter substantially equal to the inner width L of the pressure terminal 105, two problems may occur. Firstly, the wire may become shifted from the slot of the pressure terminal. Secondly, the insulation may expand outwardly in a direction perpendicular to the axis of the wire, that is, toward both the sidewalls of the pressure cutter 102, due to the pressing force. Such outward expansion of the insulation may cause the pressure cutter to expand outwardly, in the manner discussed above.
Although some pressure terminals have notches or the like in the sidewalls to allow the expanded insulation to escape, the covering material may nonetheless cause the pressure cutter to deflect outwardly since there is a practical limit to reducing the terminal size or securing sufficient strength.
For the reason stated above, design freedom decreases as the percentage of good products is decreased during the mass-production process or as the number of usable materials becomes limited. In addition, there arises a problem of preventing an increase in production cost.